Volume control system



May 18, 1937. R M. SMITH VOLUME CONTROL SYSTEM' 4 sheets-sheet 1 Filed Sept. 29, 1934 l will Ikmm, Nw

I/VI/E/V ROGERS M. f www SMITH May 18, 1937. R. M. SMITH VOLUME CONTROL SYSTEM 4 sheets-sheet 2 Filed sept. 29, 1934 I/Yl/ENToR ROGERS y. SMITH BY ATTORNEY May 18, 1937, R. M. SMITH VOLUME CONTROL SYSTEM Filed Sept. 29, 1934 4 Sheets-Sheet 3 l I/Wmak ROGERS M. SMI TH Y gf@ TRVEY May 18,1937. n. M. SMITH 2,080,581

VOLUME CONTROL SYSTEM\ Filed Sept. 29, 1934` 4 Sheets-Sheetl 4 Patented May 18, 1937 UNITED STATES PATENT OFFICEv VOLUME CONTROL SYSTEM Rogers M. Smith,

Merchantville,

by mesne assignments, to Radio Corporation of America, New York, N. Y.,

Delaware a corporation of Application September 29, 1934, Serial No. 746,078

13 Claims.

output or volume of radio receiving apparatus and the like for vehicles, in accordance with variations in speed, thereby to compensate for Variation in windage and other noises normally tendlng to interfere with reception of signals.

for radio receiving apparatus and the like'which is adapted for remote control and for operation by means responsive to variations -in speed of a vehicle in motion.

It is a further object of the presentinvention to provide an automatic speed responsive volume control system for automobile radio'receiving ap- 30 paratus and the like which is responsive to variations in speed to control vention to provide a speed responsive tone and (Cl. Z50-20) plitude of the signals transmitted without disV tortion.

The invention'will be better understood from the following description when considered in connection with the accompanying drawings and its scope will be pointed out in the appended claims. I

In the drawings Figure 1 is a schematic circuit diagram of a volume control system embodying the invention,

Fig. 2 is a similar circuit diagram showing a modification, and

Figs. 3 and 4 are also schematic circuit diagrams of combined volume and tone control systems embodying the invention.

Referring to Fig. 1, a radio receiver I having an audio frequency amplier stage II is provided with signal input and output circuits I2 and I3, respectively, and arranged to hercontrolled in gain without variation in frequency characteristic through the medium of an electric l discharge amplier device I4 having two control grids I5 and IB, a cathode I1, a Vsignal output anode I8 and suitable suppressor and screen grids I9 and-29, respectively. A

The amplifier device I4 is arranged to receive signals on one of the control grids, such as the grid I6, as shown, from the `input circuit I2 and for the purpose of transmitting the amplified signals to the output circuit I3 and the latter is coupled to the anode I 8, as indicated. The grid I9 is connected to the cathode as a suppressor and the screen grid 20 about the second control grid I5 is provided with a suitable positive biasing potential, as indicated.

The second control grid is arranged to receive a controlling potential from a variable source, responsive to speed variations. In Vthe presentf example this comprises a tapped potentiometer resistor 2|,y one end of which is connected to ground, as indicated at 22, having a variable output contact 23.

The potentiometer resistor receives a potential from a wind-driven alternating current generator 24 comprising an armature 25 connected with a propeller 26 and having a eld winding 21 as a voltage output winding.

Any suitable generator may be employed for supplying current in response to wind How. In the present example thelgenerator and propeller are mounted to receive the windage ow air stream about the vehicle and are shown in as- Y sociation with the front of an automobile, Vthe preferred location being indicated as inside or H 4 outside of the hood.

The generator output is rectified in a contact rectifier system, indicated at 28, and is suitably filtered by a shunt by-pass condenser 29 in being applied to the terminals of the potentiometer resistor 2|.

The voltage selected by adjusting the position of the contact 23 is applied to the grid I5 through shielded supply lead 30 leading from the control unit to the receiver and the lead is connected with a contact 3| of a suitable transfer switch 32 for disconnecting the remote speed control unit. In the position shown the switch 32 provides a connection from the contact 3| to a grid lead 33 leading to the grid I5. An alternate position in connection with a contact 34 provides connection for the lead 33 with the cathode I1 through the lead indicated at 35.

From the foregoing description it will be seen that the volume control system includes a variable source of potential remotely located from but connected with the receiver through a single wire lead which is preferably shielded and which may be extended any distance. The variable source of potential is responsive to speed variations or the velocity of the automobile or other vehicle through wind or air pressure operated means. In the present example this comprises a simple alternating current generator and propeller. The variable alternating current derived from the generator in response to motion of the vehicle is applied to a simple oxide or other similar type of rectifier wherein the voltage is rectified to provide direct current in a series resistor tapped for potential adjustment, as hereinafter pointed out.

A filtering means including the condenser 29 is further supplemented by a second condenser 36 preferably in the receiver and connected to the ground, as indicated, between the supply lead 30 and the return circuit of the receiver.

The operation of the system hown and described is as follows: Y

Variations in the potential applied to one of the control grids, such as the grid I5 in the present example, causes the amplification factor of' the tube I4 to vary and thereby to rchange the audio frequency gain. The controlling potential applied through the lead 30 from the remote control unit may be adjusted by the contact 23 to effect a desired volume level for a predetermined speed.. The automatic control of volume in response to speed may be provided by other speed responsive control means and the controlling potential may be applied to grids of a tube of the type` shown.

A tube of the type shown is'provided commercially by an RCA-6A? tube. A higher degree of audio frequency gain is obtained by using the inner grid I6 as the signal input grid while the other grid I5 is It will be noted that the receiver is grounded to provide a return circuit for the control potential means and that the controlling potential provided by the'control unit is positive for connection to the control lead 30 whereby the grid I5 receives an increasing positive potential with increase in speed. The increased potential serves to increase the gain of the amplifier stage withoutvintroducing distortion in the signal amplifier portion. As the rotational speed of the alternator 24 is increased coincident with the speed of the Vehicle, the generated voltage is increased so that after having been converted into direct current it is applied to the audio frequency arnpliner tube I4 to cause the gain controlling grid either of the control used as the gain' control grid.

I5 to become more positive with increase of speed. It will be noted that the cathode circuit includes a4 self-bias resistor 31 for applying a bias to the signal grid I6. This bias potential, indicated at E1, is also applied to the grid I5 through the auxiliary speed control unit and the polarity of the variable speed control unit is such that the bias potential is opposed thereto. Accordingly, the grid I5 will approach the same potential as the cathode of the tube and a higher degree of amplification is obtained from the audio frequency amplifier stage II between the input circuit I2 and the output circuit I3.

The bias control arrangement is preferably such that the additional controlling potential derived from the speed variable source such as the rectifier 28 and the generator 24 in the present example and indicated in the drawing as E2 is for maximum speed at least equal to the selfbias or other biasing potential normally applied to the grid I5 and in opposition thereto, whereby the gain controlling grid is caused to approach or equal the cathode potential when the speed is maximum. Y The switch 32 for rendering the auxiliary speed control of volume inoperative to control the receiver is arranged to connect the control grid I5 directly to the cathode when it is desired to operate the receiver or amplifier without auto-matic compensation of volume through different speeds of the vehicle. Y

For the foregoingr reasons in Fig. 1 having stage provided with an amplifier tube with two control grids in the same electric stream,Y one for receiving a signal potential to be amplified, and the other for receiving a gain controlling potential variable in accordance with changes in speed or velocity of the vehicle, is at present preferred. The selective switching means for the gain controlling grid whereby said grid is connected through a single extension lead to a grounded source of controlling potential and a self -bias resistor in the vcathode return lead providing a potential in opposition to the controlthe circuit shown circuit arrangement.

an audio frequency amplifier` For speed control of volume an audio frequency be provided with an electric discharge amplifier device in which the normal suppressor grid may be eliminated with al'm'ain signal control grid as the outer grid with shielding and ther gain controlling grid adjacent to the cathode. However, either amplifier stage may and the control grid impedance or resistor 41 through which biasing potentials are supplied to the grid 42 from a suitable self-bias resistor comprising two sectionsV 48 and 49. 'i

Signals amplified to an output circuit, indicated a suitable output connection5| by the device 40 are applied at 50, through with the anode y grid may be used in- Aterchangeably as the signal control grid. An

44 and a screen electrode 45V 42 to a suitable signal input.:r circuit, indicated at 46, and comprising'a coupling' and 59.

44. Audio frequency signals supplied by the input circuit are amplied and delivered to the output circuit under control of the second control grid 4| which is connected with control means responsive to speed variations. In the present example, the speed responsive means comprise a pivotally mounted vane arranged to receive windage currents or other air stream caused by passage of a vehicle through the air. The vane is arranged to control a potentiometer device comprising a resistance 53 and a movable contact 54 connected with the vane through the pivot point 55. A spring 5B or other suitable means connected with the contact 54 and the vane serves to provide a biasing force for moving the vane and the contact 54 in a windwise direction about the pivot point 55. The contact, therefore, is moved by the spring to the position marked Min while the windage iiow tends to overcome the spring action and move the contact in the direction of the end of the potentiometer marked MaX..

The potentiometer. resistor 53 is connected with a suitable potential source for controlling the grid 4| and in the present example is connected across the self-bias resistor section 49 in parallel therewith while the contact 54 is connected With the grid 4|, connections being made through a cable comprising three Wire connections 51, 58

It will be noted that the lead 59 is connected to ground 60 in the receiver and is connected with the shielding for the cable indicated at 6|. In order to prevent interference and undesired pickup of signals for application to the grid 4 it is preferable that the cable be shielded. The arrangement is such that as the vane 52 receives increasing pressure resulting from increasw ing speed the contact 54 is moved in a direction to decrease the negative bias on the grid 4| as derived from the resistor section 49. With the vehicle at rest and the contact 54 in the Min position the lead 51 is in effect connected with the lead 59 to provide a maximum negative bias which is reduced as the speed is increased until contact 54 is in the Max position whereby the lead 51 is connected with the lead 58. The grid connection is then at the junction point indicated at 62 between the sections 48 and 49. A reduced negative bias derived only from the resistor 49 causes an increased gain in the ampliiler stage. If desired the gain may further be increased by connecting the point S2 for the lead 58 nearer to the cathode in the circuit shown. However, in other circuits different potential supply means may be provided.

In order to increase the gain to maximum and to render the speed control means ineffective, a switch 53 is provided for connecting the leads 51 and 58 together thereby connecting the grid 4| with the point 62 of minimum negative bias for providing full gain through the amplifier stage.

In the circuit arrangement shown the controlling potential is derived from the self-bias resistance means in the cathode lead of the double grid amplier tube and is controlled by a variable resistor or potentiometer so connected with the potential source as to cause the biasing potential on the control gridvto vary in response to variations in air pressure on a movable vane. It will be noted that in this embodiment the connection with the speed control unit is made through three conductors as distinguished from a single lead required for the system shown and described in connection with Fig. 1. This system, however,

yhas the advantage that no additionalA means. is

required for providing the controlling potential and only a simple variable resistor or potentiometer is required in the remote or auxiliary volume control circuit.

Any portion or all of the potential available in the self-bias resistor means may be utilized to control the gain of the amplier stage. In the present example the grid 42 is provided with the biasing potential derived from both sections 48 and 49, whereas the gain controlling grid 4| may receive a biasing potential which varies between that provided by the resistor section 49 andthat provided by both sections.

In the control of certain radio receiving apparatus it may be preierableor desirable to utilize a single lead connection, as in the circuit of Fig. l, in connection with a simple rheostat or variable impedance having a grounded return circuit whereby a further simplified and lowl cost volume control system may be provided. A controlcircuit having these features is shown in Fig. 3, to which attention is now directed.

In Fig. 3, an audio frequency transmission circuit comprising the leads 11i-1| is provided between a combined detector amplifier tube 12 and a power output amplifier tube 13. 'I'he circuit 19-1| is connected across an output impedance device 13a in the anodel circuit 14 of the device 12 and is arranged to be variably loaded, to control the amplitude oi the signals, under control of an auxiliary control tube, indicated at 15.

The control tube 15 operates as a variable impedance device and comprises an anode 16 connected through an anode potential supply resistor 11 with the lead 1| through which anode current is taken and connected through a lead 18 and a loading condenser 19 with the lead 10 through which signals are transmitted between the tubes 12 and 13. i

The tubef15 is further provided with a cathode 88 which is connected to ground or other suitable return circuit, indicated at 9|, through a variable control resistor 82 adapted to be remotely located with respect to the resistor and arranged to be operated by a suitable Wind pressure responsive means, such as a movable Vane 83 having a pivot point 84 about which it moves. The variable contact 85 of the resistor 82 is caused to return under action of Asuitable means, such as a spring 86. The control unit is thus similar to that shown and described in connection with Fig. 2. The arm 85 is connected through a ground connection 81 to the chassis and the common circuit return lead 8|.

The tube 15 is provided with a control grid 88 Y which is connected to ground and to the negative side of the variable resistor 82 which is in eiect a variable self-bias resistor.

It will be seen that as the variable resistor 82 is caused to vary in response to changes in air pressure resulting from changes in speed of the vehicle the biasing potential on grid 88 Will vary, thereby varying the impedance of the tube, the biasing potential being increased with the increase in speed, thereby increasing the internal impedance of the tube and the loading eiect of the condenser or other reactance device 19 across the audio frequency transmission circuit, which results in. an increase in volume with increased speedand rlikewise a reduction in volume with reduced speed. l

The volumel control resistor 82 is connected with the cathode through a, switch 89 and an extension leady 98, which. is connected With a teradded at any time after installation of the re- CEIVSI.

The switch 89 is provided for causing the impedance of the tube 15 to be increased by opening the plate circuit to the cathode. The condenser load then is reduced to a minimum and the gain is increased tofmaximum.

It will further be noted in connection with Fig. 3 that the amplifier 13 supplies signals to an output device or loudspeaker 92 through an output transformer 93 and that the combined detector amplifier`12 is provided with a diode plate 93 which, in connection With the cathode, indicated at 94, serves as a rectifier and detector of incoming signals, the direct current component of which is supplied through a connection 95 for automatic volume control purposes and the alternating component of which is supplied through a variable volume control contact 96 to the control grid 91 and thence to the output circuit 14, a suitable coupling condenser 98 and a coupling resistor 99 being provided in the grid circuit. The grid 91 is supplied with a biasing potential from a suitable self-biasing resistor |00.

The speed responsive remote control means is provided as a self-bias resistor in the cathode circuit and in the case of a relatively long extension to the remote control unit a suitable bypass condenser |0| is provided across the remote control circuit comprising the lead 90 and the ground connection 9|. Y

This volume control circuit has the advantage 0f a single lead connection which is not a part of the signal conveying circuit and which does not require shielding. The circuit further permits a ground return through a simple variable resistor which itself is the self-bias resistor and the controlling potential source as well as the controlling means for volume.

The condenser 19 forl loading the audio frequency transmission circuit is preferably of such impedance that it forms a relatively low resistance path for signals to be attenuated within they audio frequency range and as a volume control means preferably attenuates signals at all audio frequencies. It is, however, frequency discriminating in thaty it forms a low impedance to the higher frequency signal and in a. relatively large capacity serv'esalso as a tone control means to reduce the signals in the high frequency end of the audio frequency range more rapidly than signals in the low audio frequency range.

The simple potentiometer control of volume thus may include the control of tone simultaneously and in response to variations in speed.

A preferred arrangement for the combined control of volume and tone is shown in Fig. 4, to which attention is now directed.

In Fig. 4, an audio frequency transmission circuit ||0 andV between a, combined detector amplifier ||2 and a second amplifier |I3, is

shown. l

The amplifier ||3 is ofthe same type as shownA in Fig. 2, having two control grids ||4 and ||5 and is provided with a self-bias resistor comcomprising a condenser ||8 and a variable impedance device provided by a tube ||9, the impedance of which is varied by variations in potential on the control grid |20. The tube is provided with a bias resistor |2| through which current flows from an anode potential supply lead |22 under control of a series resistor |23.

The gain controlling grid ||4 in the amplifier tube ||3 and the tone control grid |20 in the variable impedance device ||9 are connected to the variable contact |24 of a combined gain and tone controlling device comprising a potentiometer resistor connected in parallel across the two selfbias resistor sections ||6 and ||1 as a source of controlling potential for said grids. Movement of the contact |24 along the potentiometer resistor |25 causes a variation in potential on both grids with respect to the cathodes of said device,

thereby controlling the gain in the audio frequency amplifier channel and the tone or frequency range of the amplifier.

In the present example the arrangement is such that as Vthe contact |24 is moved clockwise the biasing potential on the grids I4 and |20 are rendered less negative, thereby increasing the gain of the amplifier and decreasing the impedance of the tone control tube ||9. This is for the reason that operation of the contact |24 gradually includes in circuit between the grid |20 and the cathode of the tube an increasing portion of the potential available across the self-bias resistors ||6 and ||1lin series with the potential available across the bias resistor |2| and in opposition thereto. A point may thus be reached to provide a maximum volume. The potentials may be balanced to provide a desired impedance at maximum volume by providing extra current through the resistor |2| from the controlling resistor |23.

A switch for rendering the'remote control and tone control devices ineffective is indicated at |21 and serves to connect the grids |20 and ||4 to the positive end of the Self-bias resistor H6, thereby increasing the gain to maximum in the tube ||3 and decreasing the impedance of the tube |9 to minimum, rendering the condenser It will be noted that the connections required i for the potentiometer device |24-|25 are the same as the circuit shown in Fig. 2 and comprise a ground lead |3| and a second lead |32 for supplying potentials to the terminal of the resistor |25 and a lead |33 from the contact |24 to the` grids ||4 and |20. The leads are preferably shielded in a cable, as indicated by the cable shield -loops |34.

The auxiliary speed control system, describedv in conjunction with Fig. 4, comprises a single control device arranged to be actuated in accordance With speed changes and preferably by a simple windage actuated vane and electric discharge device in the audio frequency circuit having control grids arranged to receive a'variable potential through operation of the control device, thereby to increase the gain of the amplifier and to reduce the high frequency response as the speed of travel increases. This is desirable, it has been found, for the reason that although the volume or sound level is increased to increase the sound output above 'the noise level caused by windage and other increasing'operating noises with increasing speed, the base or lowfrequency response is somewhat reduced in its effect upon the ear because of the heavy low frequency noises with the result that there appears to be a preponderance of high frequency response at the higher speeds of travel. Accordingly, it is found to be desirable to reduce the high frequency response, thereby to obtain an acoustic balance for pleasing tone effect, the sounds in the high frequency end of the audio frequency range being reduced to balance the unavoidable reduction or loss of low frequency sounds in the low frequency noises incidental to operation of the vehicle at the higher speeds.

From the foregoing description of several modifications of my invention its advantages should be obvious. Among these may be mentioned the fact that the sound output is always automatically correlated to vehicle speed and, consequent- 1y, to wind noise and other noises with the result that such noise does not detract from the enjoyment of musical or other types of radio programs which may be received.

Although I have chosen several modifications of my invention for purposes of explanation, other methods of and means for accomplishing the desired result; will be apparent to those skilled in the art. My invention, therefore, is not to be restricted except insofar as is necessitated by the prior art and by the spirit of the appended claims.

I I claim as my invention:

1. In a mobile sound producing system, the combination with an audio frequency amplifier, of an electric discharge amplifier device having a signal control grid, a signal input circuit connected therewith, a signal output electrode, a signal output circuit connected therewith, a cathode, means in circuit With said cathode for providing a. self-bias potential for said control grid, and a gain control grid for said device, means responsive to speed controlling a potential on said gain controlling grid, and means for deriving said potential from said self-bias resistor.

2. In a mobile sound producing apparatus, the combination with an audio frequency signal transmission circuit, of means including an electric discharge device having a gain controlling grid and gain controlling connection with said transmission circuit whereby signals transmitted by said circuit are controlled in amplitude by potentials on said grid, means for supplying a controlling potential for said grid, and means responsive to variations in air pressure resulting from variations in rate of speed of travel of said mobile apparatus for varying said potential independently of other operating potentials for said device.

3. In an audio frequency amplifier, the combination of an electric discharge device having a cathode, an anode, a control grid adjacent to the cathode, a second control grid more adjacent to the anode, a screen grid for said second control grid, circuit means for applying audio frequency signals to one of said control grids, an audio frequency output circuit connected with said anode, and means responsive to variations in speed of a vehicle in motion for controlling a of travel of a vehicle :forv

biasing potential on the other of said control grids.

4. In an audio frequency amplifier, the combination of an electric discharge device having a cathode, an anode, a control grid adjacent to the cathode, a second control grid more adjacent to the anode, a screen grid for said second control grid, circuit means for applying audio frequency signals to one of said control grids, an audio frequency output circuit connected with said anode, means responsive to variations in speed of a vehicle in motion for controlling a biasing potential on the other of said control grids, said last named means including a potentiometer device having a movable contact, said device being connected with said last named grid, and a movable vane connected with said contact to move it and being adapted to be actuated by the flow of an air stream about it resulting from operation of a vehicle carrying said apparatus.

5. In an audio frequency amplifier, the combination of an electric discharge device having a cathode, an anode, a control grid adjacent to the cathode, a second control grid more adjacent to the anode, a screen grid for said second control grid, circuit means for applying audio frequency signals to one of said control grids, an audio frequency output circuit connected with said anode, means responsive to variations in speed of a vehicle in motion for controlling a biasing potential on the other of said control grids, and means jointly controllable with said last named means for simultaneously varying'the tone characteristic of said audio frequency amplifier.

6. The combination with a radio receiver adapted for use in vehicles, of means responsive to variations in speed of a vehicle by which the said receiver is carried for simultaneously controlling the volume and tone characteristic of said receiver independently of the normal volume and tone adjustment thereof, said means including a gain controlling tube and a tone controlling tube each having a control grid, means providing a source of biasing potential for said grids, a potentiometer device connected with said potential source and with said grids to vary said potential on said grids, and a vane adapted to be actuated by air currents connected with said potentiometer to control it.

7. The combination with a radio receiver, of an audio frequency amplifier comprising an electric discharge device having a gain controlling grid, an audio frequency transmission circuit connected with said device whereby the signal amplitude therethrough is varied in accordance with variations in potential applied to said grid, and a remote control device for said receiver comprising a variable resistor connected in the cathode circuit of said electric discharge device to provide a. variable biasing means for said grid, and means responsive to the speed of a vehicle in motion, connected with said last named volume control device to actuate it in accordance with variations in said speed.

8. In an automobile radio receiver having means for controlling volume the combination with an audio frequency amplifier, of a combined gain controlling electric discharge device therein, means connected therewith providing a source of biasing potential for said device variable in accordance with variations in windage pressure about the automobile in motion to control the gain independently of said volume control means, and means for controlling the application of said potential to said device to control the gain of said amplifier independently of the first named means for controlling volume. Y 9. In a mobile sound producing apparatus, the combination with anaudio frequency amplifier, lof an electric discharge amplifier device therein having a cathode, an anode, a signal control grid and a gain control grid between said cathode and anode in the electronic stream of said device, means for applying audio frequency signals to said first named control grid, a self-bias resistor in circuit with the cathode for supplying a biasing potential to said f'lrst named control grid, and means for deriving a variable gain controlling potential from said self-bias resistor for said gain controlling grid comprising a potentiometer connected with said self-bias resistor and having a movable contact connected with said control grid and adapted to be actuated in accordance with Variations in speed of a vehicle by which said apparatus is carried.

10. In a mobile sound producing apparatus, the combination with an audio frequency amplifier ofV an electric discharge amplifier device therein having a cathode, an anode, a signal control grid and a gain control grid between said cathode and anode in the electronic stream of said device, means for applying audio frequency signals to said first named control grid, a self-bias resistor in circuit with the cathode for supplying a biasing potential to said first named control grid, means for deriving a variable gain controlling potential from said self-bias resistor for said gain controlling grid comprising a potentiometer connectedfwith said self-bias resistor and having a movable contact connected with said control grid and adapted to be actuated by variations in speed of a vehicle, craft and the like in motion, an audio frequency `signal transmission circuit, a reactancedevice and a variable impedance device connected in series across said circuit for controlling the tone of signals transmitted through said circuit, said variable impedance device comprising an electric discharge amplifier having a control grid connected with said gain controlling grid for receiving a biasing potential variation f simultaneously therewith, thereby to control the toneand volume simultaneously.

1l. The combination with an automobile radio receiver, of an Vaudio frequency amplifier having an electric discharge 'device provided Vwith a gain controlling grid and a remote volume control unit having a circuit connection with said grid, means in said remote control unit responsive to speed variation for controlling a potential in said circuit connection whereby the gain of said amplifier is varied in accordance with variations in speed of the automobile by which the receiver is carried, and means for independently adjusting said potential to provide a predetermined delay in speed control of said amplifier.

12. In a radio system for vehicles, craft and the like, an electrical sound amplifier, means for energizing said amplifier, and gain controlling means for said amplifier responsive to operation of such vehicle, craft and the like in which said system is conveyed, said amplifier including at least one electric discharge amplifier device having a signal grid and a gain controlling grid, and said gain controlling means providing a variable` grid biasing potential for said gain controlling grid and having a movable control element positioned to receive and being responsive to variations in windage fiow about said vehicle, craft and the like in motion to provide said variable potential in accordance therewith.

13. In an automotive vehicle, the combination with a radio receiver, of means for energizing said receiver, and means independent of said energizing means for varying the sound output level and tone characteristic of the receiver with variations in speed of said vehicle, said last named means including a gaine-nd tone controlling circuit for said receiver, an electrical control device therein having a movable control element, and means connected with said element to move the latter in response to variations in speed.

ROGERS M. SMITH. 

